Stellar chromospheres

Recent observational and theoretical work in the general problem of stellar chromospheres is summarized. The nature of a stellar chromosphere is reviewed, along with regions of the H-R diagram where chromospheres exist, trends emerging from semiempirical chromospheric models of single stars, and the ability of such models to match the observational data. Reasons why the Wilson-Bappu relation works are discussed, the existence of systematic flow patterns in stellar chromospheres is considered, and possible differences between chromospheres in close binaries and in single stars are examined. The general questions of chromospheric variability, the energy balance in stellar chromospheres, and the physics of chromospheric activity are described.